Method of forming metal plates with explosives



1964 M. T. ABEGG ETAL METHOD OF FORMING METAL PLATES WITH EXPLOSIVESFiled April 20, 1960 INVENTORS. MoRoNl TAYLOR ABEGG BY RICHARD ANORWOODM idww A T TORNEY.

United States Patent 3,120,327 METHOE ill WERE ENG METAL PLATES WlliiilEXPLGSEV Moroni T. Ahegg, Albuquerque, N. Mex and Richard A.

Norweod, San Biego, Caiirfi, assignors to the United fitates of Anierieaas represented by the United States Atomic Energy Commission Filed Apr.2% 19-69, Ser. No. 23,591 3 Ciai (Ci. 113 34) The present inventionrelates to a method for forming metal plates and more particularly to amethod for forming metal plates by using shaped shock waves from anexplosive charge.

The accurate forming of metal plates into contoured surfaces presents adifiicult problem when the plates are made of hard metals, e.g., highcarbon steels. Conventional dies and presses are wholly useless for thisprocess because they are not able to exert the force needed to deformmetals having low ductility and high yield stress characteristics.Conventional metal spinning processes are also incapable of shapingnon-ductile metal plates. Until recently, the only satisfactory methodfor achieving contoured hard metal plates was to machine the desiredshape out of a metal block. Machining hard metals, however, is ingeneral a tedious and time consuming process and can produce irregularlycontoured surfaces only with much difiiculty, time and expense.

The use of explosives has been recently discovered as a method forshaping otherwise unworkable metal plates into various contoured forms.Conventional methods using explosives comprise placing a metal plateover the recess of a female die and thereafter exploding a chargelocated above the plate. The shock wave from the charge has a suflicientforce to deform the metal plate into the die and cause it to take theshape thereof. This procedure is adequate so far as it shapes the plateto conform with the desired mold, but it is unsatisfactory for certainapplications in that the resulting shaped plate generally has anon-uniform thickness.

In conventional exposive forming methods a simple spherical shock waveis used for the shaping operation and consequently the metal plate isnot drawn equally from all its portions. As a result, the non-uniformelongation of the various plate portions is accordingly characterized bya non-uniform plate thickness. This nonuniform thickness is increasinglypredominant for plates of relatively small area while with plates oflarger area the non-uniformity becomes less significant.

Now a method has been discovered for shaping hard metal plates whileretaining a uniform thickness over the entire formed area. Briefly, theinvention is to effect an approximately equal drawing of all portions ofthe plate. By making the duration of pressure on each portion whilebeing drawn approximately the same on all the portions, the plate isdrawn uniformly throughout its total area. This equal distribution ofpressure duration is accomplished by shaping the shock wave from theexploded charge to register with the die such that the shock impact isdelayed on the portions Which must be drawn to a relatively greaterdepth.

Apparatus for performing this method comprises a female die having amachined recess therein. The hard metal plate to be formed is placedfiat over this recess. A flat sheet of explosive charge is centeredabove the plate and the volume enclosed between the plate and the recessis evacuated. The charge is detonated at preselected portions thereof.The explosition of the charge creates a shock Wave which travels towardsthe metal plate and wherein the shock wave is shaped to make initialcontact with the plate at portions thereof posi- 3.12%.827 Patented Feb.11, 1964 tioned over the shallowest recess surfaces. Subsequent impactsagainst the plate occur at portions thereof positioned over successivelydeeper surfaces of the recess. The plate is thus drawn in a uniformmanner and the resulting shaped plate is consequently of a uniformthickness.

Accordingly, it is a primary object of this invention to provide amethod for forming a metal plate.

It is another object of the invention to provide a method for forming ahard metal plate into a contoured shape characterized by a uniform platethickness over the entire shaped area.

Still another object is to provide an apparatus for accurtely shaping ahard metal plate with explosive charges.

A further object is to provide an apparatus for forming an explosiveshock Wave of predetermined shape.

A still further object is to provide a method of forming a uniformlythick contoured metal plate by a preselected shaped explosive shookwave.

Other objects and advantages of the invention will become apparent uponconsideration of the following description taken in conjunction with theaccompanying drawing of which:

FEGURE l is a crosssectional elevation of one apparatus used in apreferred embodiment of the invention for making hemispherical shapedplates;

FTGURE 2 is a view of section 22 in FIGURE 1 showing the arrangement ofdetonating charges; and

FIGURE 3 shows an apparatus and resulting shock wave used to form ametal plate into a convoluted configuration.

There is shown in FIGURE 1 an apparatus 11 which is used in forming ahard metal plate into a hemispherical shell. A block die 12 has ahemispherical recess 13 formed in a surface 14 thereof. Die 12 is madeof an epoxy plastic material reinforced with fiberglass. Although theuse of a hard tool steel die is possible, the epoxy material ispreferable because of its expendability and relative low cost.Repetitive use of the die tends to roughen and deteriorate the surfaceof the recess thus making periodic replacement necessary. The problem ofdeterioration is somewhat reduced by lubricating the recess surface, butthe number of drawing operations on the die is somewhat limited.

A metal plate 16 which is to be formed into a hemisphericalconfiguration is placed on surface 14 over the recess 13. A rounded edge1'7 is formed at the juncture of recess 13 and surface 14- to preventthe plate from be ing sheared during the forming operation. Resting onsurface 14 and concentric with recess 13 is a short tubular cylinder 13.The upper open end of cylinder 18 supports a block 19 and also formsvertical walls enclosing a chamber 2.1. A vacuum seal 22 is formedbetween the lower end of cylinder 18 and die 12. Another vacuum seal 23is situated between the upper end of cylinder 18 and block 19. Chamber21 and recess 13 are evacuated by a vacuum line 24 which connectsthrough cylinder 13.

A disk of explosive charge 26 is suspended above plate 16 on the undersurface 27 of block 19 and disk 26 is centered over the hemisphericalrecess i3. Referring now also to FIG RE 2, a circular groove 28 isrecessed into surface 27 of block 19, groove 28 having a diameterslightly larger than that of die hemisphere 13. The groove 28 is fdledwith an explosive material 29* so that the material contacts aperipheral region of charge disk 26. A plurality of cylindrical bores 31communicate from evenly spaced points along groove 28 to common junction32 situated in the upper portion of block l9, common junction 32 beingcoincident with an axis passing through the center of explosive disk 26.A bore 33 extends perpendicularly downwards from a top surface 3 ofblock 19 and connects to junction The bores 31 are equal in length andare all filled with an explosive material 36. Bore 33 contains thereinan explosive detonator 3'7. A small hole 38 is made in the center ofcharge dish 26 to prevent jetting when the implosion of disk 26 reachesthe center thereof. Dashed line 3% designates the resulting shock wavefront created upon detonation of explosive charge 26.

in operation, the detonator 37 is fired which in turn simultaneouslyignites the explosive charges as at junction 32. Charges 35 all burnexplosively at the same rate thus explosive ring 29 is simultaneouslydetonated at all juncture points with charges as. Explosive ring 29detonates the charge disk 26 around a circle near its periphery andcauses the disk to start burning radially inward and outward therefrom.The shock wave 39 caused by the detonation of charge disl: as has aleading peripheral portion traveling towards the edge of recess 13.Because the center of dish 2r; is ignited at a later time than theperiphery, the center portion of the shock wtve is delayed behind theinitial peripheral portion. The resulting shock wave is thus shaped asshown by dashed line 39.

The shaped shocl' wave 39 makes initial impact against plate 16 near theedge 1? of recess l3. Hence, the drawing or elongation of plate 15 alsoinitially begun near the edge l7. Subsequent impact against the platetakes place progressively into the center portion thereof. The plate isthus drawn first at the edges and then, in sequence, at portions closerto the center. As a result, the impacting forces on the centermostportions are accordingly delayed and an equal drawing of all portions iseffected. The evacuation of recess 13 serves to reduce pressureresistance on the underside of the plate thus cont .buting to theprevention of non uniform ics in the finished plate.

Recess 13 is most readily evacuated by evacuating chamber 21 which thendraws from the recess thereby creating a vacuum in both the chamber andrecess. However, to increase the coupling between the explosive shockwave and the plate the recess can be sealed off from chamber 21 and thechamber then filled with air to atmospheric pressure. Even greater shockwave coupling is effected by filling the chamber with a liquid after theevacuated recess is sealed off from the chamber. When using a shockcoupling liquid conventional sealing means are employed be Ween theplate and top surface of the die to preserve the vacuum in the recess.

it should be understood that the present invention is an applicablemethod and apparatus for shaping metal plates into various contouredconfigurations other than the above-described hemispherical form. Forinstance, FIGURE 3 illustrates an apparatus for forming a convolutedplate. There is shown therein a die 41 having a contoured recess 42 inthe top surface 43 thereof. Recessed surface 42 is a surface ofrevolution about a central axis perpendicular to surface .3, and a metalplate 44 is placed on surfiace 43 over recess 42. A cylinder 46separates die il from a block 47. A disk of explosive charge 4-8 issuspended above plate 24 on the underside surface of blocl: 17. Acircular groove 51 is recessed into surface of block 4 7 and a ring ofexplosive charge material 52 is filled into groove fill to contactcharge disk 4%. A plurality of cylindrical bores 53' connect to groove51 and incline inwardly therefrom to a common junction 54. A verticalbore 56 connects junction 54 to the center of disk Another vertical bore57 extends downward from the top surface s of lose 47 and a detonator 55contained therein connects into junction 54. The bores 53 are all filledwith an explosive charge material 61 to contact both charge material 52and detonator 5'9. Another explosive charge material 62 fills verticalbore 55 to connect junction 54 to the center portion of charge dislt Acircular ring 63 of non-explosive material separates charge disk 48 (iinto an inner and outer portion. Ring 63 serves to prevent jetting ratthe juncture where the explosion initiated at the center of disk &3meets the explosion originating at the periphery of disk in operationthe detonator 59 is fired which in turn ignites the charge materials 52and 62. at junction 54. Charge material 62 is sel c ed from a properexplosive mixture and burns at a slower rate than material 52 in orderthat the periphery of charge disk 48 be ignited slightly before thecenter portion thereof. it should be noted that various compositions ofsolid explosives are commercially available having varied rates ofburning. Hence it is apparent that by properly selecting the borepositions and charge materials a shock wave of virtually any shape canbe created. The subsequent explosion of charge disk 48 results in asiaped shock wave front designated by dashed line 64. As defined by theprinciple of the invention, this shock wave impacts against successiveselected portions of plate such that the shallower portions are drawnprior to the deeper portions as discussed in hemispherical drawing,supra.

The procedure and results of an actual experiment are now cited as aspecific example of both the method and apparatus of the presentinvention. The apparatus used is illustrated in FIGURES 1 and 2 andcomprised a cubic die one foot on an edge made of fiberglass reinforcedepoxy resin. The hemispherical recess therein had a radius of one inch,with the edge thereof rounded in a radius of one-eighth of an inch. Aone-eighth inch thick plate four inches square made of type 302stainless steel was placed over the hemi pherical recess. The explosivecharge disk was a solid high explosive composition consisting of 60% RDXand 40% TNT bonded together by wax. Such explosive is commonlydesignated as composition B and was one-eighth of an inch thicx and fourinches in diameter. The charge material in the cylindrical bores was ahigh explosive consisting of 92% RDX and 8% isobutylene polymer commonlyknown as composition (3-4. The vacuum chamber and recess were reduced inpressure to five inches of mercury. The initiator was ignited and theexplosive charge was detonated. Following the detonation of theexplosive disk, the steel plate was removed from the recess of the dieand observed to have taken the exact shape of the hemispherical recess.The thickness of the formed hemispherical shell was observed to havebeen uniform over its entire area to within an accuracy of fiveone-thousandths of an inch.

It is of special note that the operation of the present inventiondepends upon the deformation of a fiat metal plate by a shaped explosiveshock wave, wherein the shock wave is best described as being aproportionately inverted image of the die recess configuration intowhich the plate is to be pressed. The shock wave need not be a mirrorimage of the die recess but it should be curved approximately inproportion to the die configuration and inverted thereto.

It is to be observed that many possible shaped plate configurations canbe formed by the present invention. The invention is readily applicablefor creating shaped plates in the form of parabolas, cones, hyperbolas,etc., and an unlimited number of variations thereof. The detaileddescription given herein is by way of description and illustration onlyand is not to be taken by way of limitation, the spirit and scope ofthis invention being limited only by the terms of the appended claims.

What is claimed is:

1. In a method for shaping a fiat metal plate into a contoured surfaceusing explosive shock waves, the steps comprising placing said metalplate over a contoured recess of a female die, shaping an explosiveshock wave in a configuration essentially inverted to the configurationof said contoured recess, disposing said shock waves to travel towardssaid recess in a mirror relation thereto, and impacting said shock wavesagainst said metal plate.

2. In a method for shaping a flat metal plate into a contoured surfaceusing explosive shock waves, the steps comprising placing said plateover a contoured recess of a female die, evacuating the volume definedby said recess and said plate, shaping an explosive shock wave in aconfiguration essentially inverted to the configuration of saidcontoured recess, disposing said shock wave to travel towards saidrecess in mirror relation thereto, and im pacting said shock wavesagainst said metal plate.

3. in a method for forming a flat metal plate into a contoured surfaceusing explosive shock waves, the steps comprising placing said plateover a contoured recess of a female die, evacuating the volume definedby said recess and said plate, shaping an explosive shock wave in aconfiguration essentially inverted to the configuration of saidcontoured recess, disposing said shock wave to travel towards saidrecess in mirror relation thereto, impacting said shock waves againstsaid metal plate, forcing said plate against said recess, and removingthe shaped plate from said recess.

4. In a method for forming a flat metal plate into a contoured surfaceusing explosive shock waves, the steps comprising placing said plateover a contoured recess of a female die, evacuating the volume definedby said recess and said plate, shaping an explosive shock wave in aconfiguration essentially inverted to the configuration of saidcontoured recess, disposing said shock wave to travel through a liquidcoupling fluid towards said recess in a mirror relation thereto,impacting said shock waves against said metal plate, forcing said plateagainst said recess, and removing the shaped plate from said recess.

5. In a method for shaping a flat metal plate into a contoured surfaceusing explosive shock waves, the steps comprising placing said plateover a contoured recessed surface of a female die having relativelyshallower and deeper portions, impacting against said plate a shock waveshaped to apply initial forces on portions of said plate disposed overthe relatively shallowest portions of said recess and to applysuccessive forces on portions of said plate disposed over successivelydeeper portions of said recess, forcing said plate into the form of saidrecessed surface by said shock wave, and removing the formed plate fromsaid recess.

6. In a method for shaping a fiat metal plate into a contoured surfaceusing explosive shock waves, the steps comprising placing said plateover a contoured recessed surface of a female die having relativelyshallower and deeper portions, evacuating the volume defined by saidplate and said recess, disposing a shock coupling fluid adjacent to theexposed side of said plate, impacting an initial explosive shock forceagainst said plate on portions thereof disposed over the relativelyshallowest portions of said recess, impacting successive subsequentshock forces against portions of said plate disposed over successivelydeeper portions of said recess, forcing said plate into the form of saidrecessed surface by said shock forces, and removing the formed platefrom said recess.

7. In a method for shaping a flat metal plate into a contoured surfaceusing explosive shock waves, the steps comprising placing said plateover a contoured recessed surface of a female die having relativelyshallower and deeper portions, evacuating the volume defined by saidplate and said recess, disposing a sheet of explosive charge above saidplate parallel thereto and spaced apart therefrom, disposing a shockcoupling fluid between said plate and said explosive sheet, detonatingsaid sheet at portions thereof in opposition to the relativelyshallowest portions of said recessed surface, shaping an explosive shockwave by said detonation in a configuration essentially inverted to theconfiguration of said contoured recess, conducting said shock wavethrough said coupling fluid towards said recess in a mirror relationthereto, impacting the leading portions of said shock wave against saidplate at portions thereof disposed over the relatively shallowestportions of said recess, impacting successive subsequent forces fromsaid shock wave against portions of said plate disposed oversuccessively deeper portions of said recess, forcing said plate into theform of said recess by said shock wave, and removing the formed platefrom said recess.

8. In a method utilizing explosive shock Waves for shaping a flat metalplate into a hemispherical surface, the steps comprising placing saidplate over a hemispherical recessed surface in a female die, shaping anexplosive shock wave into an essentially hemispherical configuration,evacuating the volume defined by said recess and said plate, disposingsaid shock wave to travel towards said recess in a mirror relationthereto, impacting said shock :wave against said metal plate, forcingsaid plate against said recessed surface, and removing the formed platefrom said recess.

References Cited in the file of this patent UNITED STATES PATENTS2,754,786 Schulze et al July 17, 1956 2,757,750 Hawkins et a1. Aug. 7,1956 2,761,404 Moller Sept. 4, 1956 2,839,997 Church et al June 24, 19582,900,905 MacDougall Aug. 25, 1959 2,929,345 Zityko Mar. 22, 19602,943,587 Samuelsson July 5, 1960 2,969,758 Howlett et a1. Jan. 31, 1961FOREIGN PATENTS 637,332 Great Britain May 17, 1950 766,741 Great BritainIan. 23, 1957

1. IN A METHOD FOR SHAPING A FLAT METAL PLATE INTO A CONTOURED SURFACEUSING EXPLOSIVE SHOCK WAVES, THE STEPS COMPRISING PLACING SAID METALPLATE OVER A CONTOURED RECESS OF A FEMALE DIE, SHAPING AN EXPLOSIVESHOCK WAVE IN A CONFIGURATION ESSENTIALLY INVERTED TO THE CONFIGURATIONOF SAID CONTOURED RECESS, DISPOSING SAID SHOCK WAVES TO TRAVEL TOWARDSSAID RECESS IN A MIRROR RELATION THERETO, AND IMPACTING SAID SHOCK WAVESAGAINST SAID METAL PLATE.